1. Field of the Invention
This invention relates to a photosensitive material or an image recording material, more particularly, to a photosensitive material or image recording material containing a cobalt complex salt, and a new image forming process employing such photosensitive material or image recording material. More specifically, this invention relates to a color photosensitive material, an image recording material, and a color image forming process.
2. Description of the Prior Art
In the field of color photography to which this invention belongs, a color photographic material which comprises a support which is coated with a silver halide emulsion which has a cyan coupler, a yellow coupler or a magenta coupler contained therein in various manners is imagewise exposed and subjected to a series of processing steps for reproducing an image in the photographic material.
These processing steps generally consist of a color developing step and a desilvering step. In the color developing step the exposed silver halide is reduced with a color developing agent to form silver and the oxidized color developing agent reacts with a coupler to provide a dye image. Thereafter, the color photographic material is transferred to the desilvering step where the silver produced in the color developing step is oxidized with an oxidant (generally referred to as a bleaching agent), and is then dissolved by means of a silver ion chelating agent (which is generally referred to as a fixing agent) and removed from the photographic material. As a result, only a dye image is formed on the photographic material. In practice, the color developing and desilvering steps are accompanied by auxiliary steps for preserving the photographic and physical quality of the image or for improving the stability of the image. These auxiliary steps include the use of a hardening solution for preventing excessive softening of the photosensitive layer under processing, a stop solution for effectively stopping the development reaction, an image stabilizing solution for stabilizing the image, and a solution for removing the anti-halation backing from the support.
A color photographic material processing method of this type has been commonly employed in the industry worldwide since the 1940's. The color photosensitive material used in this color processing usually contains about 1 to 15 g of silver (as silver halide) per 1 m.sup.2 of the material. Most reflex image materials typified by a color paper contain 1 to 2.5 g of silver per 1 m.sup.2 of the material, whereas most light-sensitive materials for taking photographs such as a color negative film or color reversal film contain 3 to 9 g of silver. While this amount of silver is necessary to provide the desired color image density, a lesser amount would prove a great benefit in terms of saving silver resources as well as processing costs.
One method of reducing the amount of silver halide in the photosensitive material is described in U.S. Pat. Nos. 3,826,652, 3,834,907, 3,856,524, 3,862,842, 3,923,511, 3,970,458 and 4,002,477 wherein the object is achieved by a new color intensification process. According to the specification of the prior art reference, nuclei distributed imagewise serve as a catalyst for oxidation of a cobalt complex compound to form a dye, hence a color image. Since the nuclei are present as a catalyst, only a very small amount of them is used, and therefore, in the case of silver, a far smaller amount of silver salt than is used in a conventional silver salt gelatin emulsion can achieve the desired color density. In this case, the cobalt complex compound is used in forming the imagewise distributed nuclei, more specifically, in an intensifying step following color or black-and-white development. Alternatively if desired, it may be added to the developing solution and used in the nucleus forming step. In the former case, addition of the intensifying step renders the entire processing sequence longer, and in the latter case, the cobalt complex salt remains stable only for a very short period of time in a reducing atmosphere of high pH. Therefore, commercialization of this process requires not only making the processing sequence simple and rapid but also improving the stability of the processing solution.
It is also known in the art of color photography to add a cobalt (III) salt to a silver halide photosensitive material. The addition of a cobalt salt to a photosensitive material as a stabilizer or anti-foggant is disclosed in British Pat. No. 1,214,982, according to which a chelated compound produced by reacting cobalt (II) or manganese (II) with aminopolycarboxylic acid is added to the photosensitive material to thereby prevent fogging and increase the stability of the image. However, the cobalt salt in the British Patent is used in such a small amount it hardly functions as an intensifying agent.
In general, when a large amount of cobalt salt is present in the photosensitive material it considerably lowers sensitivity. Therefore, several methods have been proposed for incorporating a cobalt salt in the photosensitive material such that it exhibits an intensifying effect without causing an excessive decrease in the sensitivity. British Pat. No. 1,456,542 discloses a method of adding a water soluble cobalt (III) complex having as a counter ion, a polyatomic anion like a carbonate ion, a sulfate ion or an acetate ion. U.S. Pat. No. 3,847,619 discloses forming a water insoluble cobalt (III) complex whose ion is a counter ion to the ion of a high molecular weight organic compound and incorporating the complex into a photosensitive material.
Indeed, introducing a cobalt (III) complex into a photosensitive material as a counter ion to the ion of a high molecular weight organic compound is an effective means of containing a high concentration of cobalt (III) complex in the photosensitive material and stabilizing it until the photosensitive material is used. However, as pointed out in British Pat. No. 1,461,892, this process has two defects. The first defect is its inability to limit the decrease in sensitivity to a satisfactorily low level. As is frequently observed, when a strong oxidant such as a water soluble cobalt (III) complex contacts the photosensitive silver halide grains, the latent image speck of silver halide grains formed upon exposure to light, that is the cluster of silver atoms which is produced when the silver halide is reduced by light, is oxidized and destroyed by the cobalt (III) complex. To overcome this defect, the British Pat. No. 1,461,892 discloses a technique in which both the cobalt (III) complex and a tetrazaindene compound are present in the photosensitive material, but the result is not as good as desired and the decrease in sensitivity cannot be held to a commercially acceptable level.
Even if the cobalt complex is contained in a non-sensitive layer free from silver halide, it inevitably adversely affects the photosensitive layer since, as the non-sensitive layer is coated on the photosensitive layer, the complex migrates between the layers with water as a medium and reaches the photosensitive layer. Research Disclosure, Vol. 136, pp. 24-25, No. 13,630, August 1975 describes a method wherein a compound consisting of a water soluble color coupler and a water soluble hexamine cobalt (III) ion as a counter ion for the water soluble color coupler is dispersed in an aqueous solution of gelatin, the resulting dispersion being then added to a silver halide emulsion. This Research Disclosure also reports a method wherein a compound consisting of a color coupler and a hexamine cobalt (III) ion as a counter ion for the color coupler is disclosed in a mixture of triethyl phosphate and di-n-butyl phthalate, the resulting solution is dispersed in an aqueous solution of gelatin, and the dispersion obtained is then added to a silver halide emulsion. However, the cobalt (III) compound is easily dissociated into the cobalt (III) ion and color coupler ion, which are counter ions to each other, and thus fails to limit the decrease in sensitivity to a desirable extent. In addition, the cobalt (III) ion is released from the compound in the initial stage of development and so, it is transferred to the developing solution before completion of the development. As a consequence, only a small intensifying effect is achieved with the cobalt (III) ion. In addition, use of a color coupler, which is a counter ion for the cobalt (III) ion, as an agent to form a color requires addition of the ion paired compound consisting of the cobalt (III) ion and coupler in a light-sensitive layer. Consequently, so long as the method described in Research Disclosure, Vol. 136, pp. 24-25, No. 13,630, August 1965 is employed, the cobalt (III) complex cannot be added to a non-sensitive layer to mitigate any adverse effect due to the cobalt (III) ion of the cobalt (III) complex having the coupler as a counter ion.
The second defect of the process described in British Pat. No. 1,461,892 is that it provides a cobalt (III) complex containing photosensitive material in which photographic properties such as sensitivity deteriorate very easily during storage. It is generally required that a prepared photosensitive material maintain a certain level of photographic properties until use. However, the conventional cobalt (III) complex containing photosensitive material suffers considerable deterioration of its photographic properties during storage, perhaps due to a change in the properties of the silver halide grains or to the change in the cobalt (III) complex as a result of reaction with materials present in the photosensitive material together with said complex. The state of the art is such that none of the methods described in the above references in which a cobalt (III) complex is incorporated in a photosensitive material provides a photosensitive material which retains its photographic properties stably for a normally required period of time.